Abstract

JSON is a useful data serialization and messaging format.
This specification defines JSON-LD 1.1, a JSON-based format to serialize
Linked Data. The syntax is designed to easily integrate into deployed
systems that already use JSON, and provides a smooth upgrade path from
JSON to JSON-LD.
It is primarily intended to be a way to use Linked Data in Web-based
programming environments, to build interoperable Web services, and to
store Linked Data in JSON-based storage engines.

This specification describes a superset of the features defined in
JSON-LD 1.0 [JSON-LD10]
and, except where noted,
documents created using the 1.0 version of this specification remain compatible with JSON-LD 1.1.

Status of This Document

This section describes the status of this
document at the time of its publication. Other documents may supersede
this document. A list of current W3C publications and the latest revision
of this technical report can be found in the
W3C technical reports index at
https://www.w3.org/TR/.

W3C publishes a Candidate Recommendation to indicate that the document is believed to be
stable and to encourage implementation by the developer community. This Candidate
Recommendation is expected to advance to Proposed Recommendation no earlier than
03 April 2020.

Publication as a Candidate Recommendation does not imply endorsement by the W3C
Membership. This is a draft document and may be updated, replaced or
obsoleted by other documents at any time. It is inappropriate to cite this
document as other than work in progress.

1. Introduction

This section is non-normative.

Linked Data [LINKED-DATA] is a way to create a network of
standards-based machine interpretable data across different documents and
Web sites. It allows an application to start at one piece of Linked Data,
and follow embedded links to other pieces of Linked Data that are hosted on
different sites across the Web.

JSON-LD is a lightweight syntax to serialize Linked Data in
JSON [RFC8259]. Its design allows existing JSON to be interpreted as
Linked Data with minimal changes. JSON-LD is primarily intended to be a
way to use Linked Data in Web-based programming environments, to build
interoperable Web services, and to store Linked Data in JSON-based storage engines. Since
JSON-LD is 100% compatible with JSON, the large number of JSON parsers and libraries
available today can be reused. In addition to all the features JSON provides,
JSON-LD introduces:

and a facility to express one or more directed graphs, such as a social
network, in a single document.

JSON-LD is designed to be usable directly as JSON, with no knowledge of RDF
[RDF11-CONCEPTS]. It is also designed to be usable as RDF
in conjunction with other Linked Data technologies like SPARQL [SPARQL11-OVERVIEW].
Developers who
require any of the facilities listed above or need to serialize an RDF graph
or Dataset in a JSON-based syntax will find JSON-LD of interest. People
intending to use JSON-LD with RDF tools will find it can be used as another
RDF syntax, as with [Turtle] and [TriG]. Complete details of how JSON-LD relates
to RDF are in section § 10. Relationship to RDF.

The syntax is designed to not disturb already
deployed systems running on JSON, but provide a smooth upgrade path from
JSON to JSON-LD. Since the shape of such data varies wildly, JSON-LD
features mechanisms to reshape documents into a deterministic structure
which simplifies their processing.

1.1 How to Read this Document

This section is non-normative.

This document is a detailed specification for a serialization of Linked
Data in JSON. The document is primarily intended for the following audiences:

Software developers who want to encode Linked Data in a variety of
programming languages that can use JSON

Software developers who want to convert existing JSON to JSON-LD

Software developers who want to understand the design decisions and
language syntax for JSON-LD

Software developers who want to implement processors and APIs for
JSON-LD

Software developers who want to generate or consume Linked Data,
an RDF graph, or an RDF Dataset in a JSON syntax

A companion document, the JSON-LD 1.1 Processing Algorithms and API specification
[JSON-LD11-API], specifies how to work with JSON-LD at a higher level by
providing a standard library interface for common JSON-LD operations.

To understand the basics in this specification you must first be familiar with
JSON, which is detailed in [RFC8259].

This document almost exclusively uses the term IRI
(Internationalized Resource Indicator)
when discussing hyperlinks. Many Web developers are more familiar with the
URL (Uniform Resource Locator)
terminology. The document also uses, albeit rarely, the URI
(Uniform Resource Indicator)
terminology. While these terms are often used interchangeably among
technical communities, they do have important distinctions from one
another and the specification goes to great lengths to try and use the
proper terminology at all times.

This document can highlight changes since the JSON-LD 1.0 version.
Select to changes.

1.2 Contributing

This section is non-normative.

There are a number of ways that one may participate in the development of
this specification:

Examples are in light khaki boxes, with khaki left border,
and with a numbered "Example" header in khaki.
Examples are always informative. The content of the example is in monospace font and may be syntax colored.
Examples may have tabbed navigation buttons
to show the results of transforming an example into other representations.

1.4 Terminology

This section is non-normative.

This document uses the following terms as defined in external specifications
and defines terms specific to JSON-LD.

Terms imported from Other Specifications

In the JSON serialization,
an array structure is represented as square brackets surrounding zero or more values.
Values are separated by commas.
In the internal representation,
a list (also called an array) is an ordered collection of zero or more values.
While JSON-LD uses the same array representation as JSON,
the collection is unordered by default.
While order is preserved in regular JSON arrays,
it is not in regular JSON-LD arrays unless specifically defined
(see the Sets and Lists section of JSON-LD 1.1.

In the JSON serialization,
an object structure
is represented as a pair of curly brackets surrounding zero or more name/value pairs (or members).
A name is a string.
A single colon comes after each name,
separating the name from the value.
A single comma separates a value from a following name.
In JSON-LD the names in an object must be unique.

The use of the null value within JSON-LD
is used to ignore or reset values.
A map entry in the @context where the value,
or the @id of the value, is null,
explicitly decouples a term's association with an IRI.
A map entry in the body of a JSON-LD document
whose value is null
has the same meaning as if the map entry was not defined.
If @value, @list, or @set is set to null in expanded form,
then the entire JSON object is ignored.

In the JSON serialization, a number
is similar to that used in most programming languages,
except that the octal and hexadecimal formats are not used and that leading zeros are not allowed.
In the internal representation,
a number is equivalent to either a long
or double,
depending on if the number has a non-zero fractional part (see [WEBIDL]).

A node in a graph that is neither an IRI,
nor a literal.
A blank node does not contain
a de-referenceable identifier because it is either ephemeral in nature
or does not contain information that needs to be linked to from outside of the linked data graph.
In JSON-LD,
a blank node is assigned an identifier starting with the prefix _:.

JSON-LD Specific Term Definitions

active context

A context that is used to resolve terms
while the processing algorithm is running.

base direction

The base direction is the direction used when a string does not have a direction associated with it directly.
It can be set in the context using the @direction key
whose value must be one of the strings "ltr", "rtl", or null.
See the Context Definitions section of JSON-LD 1.1 for a normative description.

compact IRI

A compact IRI has the form of prefix:suffix
and is used as a way of expressing an IRI without needing to define separate term definitions
for each IRI contained within a common vocabulary identified by prefix.

The default language is the language used when a string does not have a language associated with it directly.
It can be set in the context using the @language key
whose value must be a string representing a [BCP47] language code or null.
See the Context Definitions section of JSON-LD 1.1 for a normative description.

An expanded term definition is a term definition
where the value is a map
containing one or more keyword keys to define the associated IRI,
if this is a reverse property,
the type associated with string values, and a container mapping.
See the Expanded Term Definition section of JSON-LD 1.1 for a normative description.

A JSON-LD document,
which describes the form for transforming another JSON-LD document
using matching and embedding rules.
A frame document allows additional keywords and certain map entries
to describe the matching and transforming process.

An id map is a map value of a term
defined with @container set to @id.
The values of the id map must be node objects,
and its keys are interpreted as IRIs representing
the @id of the associated node object.
If a value in the id map contains a key expanding to @id,
its value must be equivalent to the referencing key in the id map.
See the Id Maps section of JSON-LD 1.1 for a normative description.

The JSON-LD internal representation
is the result of transforming a JSON syntactic structure
into the core data structures suitable for direct processing:
arrays, maps, strings, numbers, booleans, and null.

An language map is a map value of a term
defined with @container set to @language,
whose keys must be strings representing [BCP47] language codes
and the values must be any of the following types:
null,
string, or
an array of zero or more of the above possibilities.
See the Language Maps section of JSON-LD 1.1 for a normative description.

The processing mode defines how a JSON-LD document is processed.
By default, all documents are assumed to be conformant with this specification.
By defining a different version using the @versionentry in a context,
publishers can ensure that processors conformant with JSON-LD 1.0 [JSON-LD10]
will not accidentally process JSON-LD 1.1 documents, possibly creating a different output.
The API provides an option for setting the processing mode to json-ld-1.0,
which will prevent JSON-LD 1.1 features from being activated,
or error if @versionentry in a context is explicitly set to 1.1.
This specification extends JSON-LD 1.0
via the json-ld-1.1processing mode.

A term is a short word defined in a context
that may be expanded to an IRI.
See the Terms section of JSON-LD 1.1 for a normative description.

term definition

A term definition is an entry in a context,
where the key defines a term
which may be used within a map
as a key, type, or elsewhere that a string is interpreted as a vocabulary item.
Its value is either a string (simple term definition),
expanding to an IRI,
or a map (expanded term definition).

type map

A type map is a map value of a term
defined with @container set to @type,
whose keys are interpreted as IRIs
representing the @type of the associated node object;
the value must be a node object, or array of node objects.
If the value contains a term expanding to @type,
its values are merged with the map value when expanding.
See the Type Maps section of JSON-LD 1.1 for a normative description.

1.5 Design Goals and Rationale

This section is non-normative.

JSON-LD satisfies the following design goals:

Simplicity

No extra processors or software libraries are necessary to use JSON-LD
in its most basic form. The language provides developers with a very easy
learning curve. Developers not concerned with Linked Data only need to understand JSON,
and know to include but ignore the @context property,
to use the basic functionality in JSON-LD.

Compatibility

A JSON-LD document is always a valid JSON document. This ensures that
all of the standard JSON libraries work seamlessly with JSON-LD documents.

Expressiveness

The syntax serializes labeled directed graphs. This ensures that almost
every real world data model can be expressed.

Terseness

The JSON-LD syntax is very terse and human readable, requiring as
little effort as possible from the developer.

Zero Edits, most of the time

JSON-LD ensures a smooth and simple transition from existing
JSON-based systems. In many cases,
zero edits to the JSON document and the addition of one line to the HTTP response
should suffice (see § 6.1 Interpreting JSON as JSON-LD).
This allows organizations that have
already deployed large JSON-based infrastructure to use JSON-LD's features
in a way that is not disruptive to their day-to-day operations and is
transparent to their current customers. However, there are times where
mapping JSON to a graph representation is a complex undertaking.
In these instances, rather than extending JSON-LD to support
esoteric use cases, we chose not to support the use case. While Zero
Edits is a design goal, it is not always possible without adding
great complexity to the language. JSON-LD focuses on simplicity when
possible.

Usable as RDF

JSON-LD is usable by developers as
idiomatic JSON, with no need to understand RDF [RDF11-CONCEPTS].
JSON-LD is also usable as RDF, so people intending to use JSON-LD
with RDF tools will find it can be used like any other RDF syntax.
Complete details of how JSON-LD relates to RDF are in section
§ 10. Relationship to RDF.

Within a directed graph, nodes are resources, and may
be unnamed, i.e., not identified by an IRI;
which are called blank nodes,
and may be identified using a blank node identifier.
These identifiers may be required to represent a fully connected graph
using a tree structure, such as JSON, but otherwise have no
intrinsic meaning.
Literal values, such as strings and numbers, are also considered resources,
and JSON-LD distinguishes between node objects and value objects to distinguish between the different
kinds of resource.

This simple data model is incredibly
flexible and powerful, capable of modeling almost any kind of
data. For a deeper explanation of the data model, see
section § 8. Data Model.

Developers who are familiar with Linked Data technologies will
recognize the data model as the RDF Data Model. To dive deeper into how
JSON-LD and RDF are related, see
section § 10. Relationship to RDF.

Used to define the short-hand names that are used throughout a JSON-LD
document. These short-hand names are called terms and help
developers to express specific identifiers in a compact manner. The
@context keyword is described in detail in
§ 3.1 The Context.

Used to express an ordered set of data.
This keyword is described in § 4.3.1 Lists.

@nest

Used to define a property of a node object that groups together properties of that node, but is not an edge in the graph.

@none

Used as an index value
in an index map, id map, language map, type map, or elsewhere where a map is
used to index into other values, when the indexed node does not have the feature being indexed.

@prefix

With the value true, allows this term to be used to construct a compact IRI
when compacting.
With the value false prevents the term from being used to construct a compact IRI.
Also determines if the term will be considered when expanding compact IRIs.

@propagate

Used in a context definition to change the scope of that context.
By default, it is true,
meaning that contexts propagate across node objects
(other than for type-scoped contexts, which default to false).
Setting this to false causes term definitions created within that context
to be removed when entering a new node object.

The use of @type to define a type for both
node objects and value objects addresses the basic need to type data,
be it a literal value or a more complicated resource.
Experts may find the overloaded use of the @type keyword for both purposes concerning,
but should note that Web developer usage of this feature over multiple years
has not resulted in its misuse due to the far less frequent use of @type
to express typed literal values.

Within a context definition@version takes the specific value 1.1, not
"json-ld-1.1", as a JSON-LD 1.0 processor may accept a string value for @version,
but will reject a numeric value.

Note

The use of 1.1 for the value of @version is intended to
cause a JSON-LD 1.0 processor to stop processing.
Although it is clearly meant to be related to JSON-LD 1.1, it does not
otherwise adhere to the requirements for Semantic Versioning.

2. Conformance

As well as sections marked as non-normative, all authoring guidelines, diagrams, examples, and notes in this specification are non-normative. Everything else in this specification is normative.

The key words MAY, MUST, MUST NOT, RECOMMENDED, SHOULD, and SHOULD NOT in this document
are to be interpreted as described in
BCP 14
[RFC2119] [RFC8174]
when, and only when, they appear in all capitals, as shown here.

A JSON-LD document complies with this specification if it follows
the normative statements in appendix § 9. JSON-LD Grammar. JSON documents
can be interpreted as JSON-LD by following the normative statements in
§ 6.1 Interpreting JSON as JSON-LD. For convenience, normative
statements for documents are often phrased as statements on the properties of the document.

This specification makes use of the following namespace prefixes:

Prefix

IRI

dc11

http://purl.org/dc/elements/1.1/

dcterms

http://purl.org/dc/terms/

cred

https://w3id.org/credentials#

foaf

http://xmlns.com/foaf/0.1/

geojson

https://purl.org/geojson/vocab#

prov

http://www.w3.org/ns/prov#

i18n

https://www.w3.org/ns/i18n#

rdf

http://www.w3.org/1999/02/22-rdf-syntax-ns#

schema

http://schema.org/

skos

http://www.w3.org/2004/02/skos/core#

xsd

http://www.w3.org/2001/XMLSchema#

These are used within this document as part of a compact IRI
as a shorthand for the resulting IRI, such as dcterms:title
used to represent http://purl.org/dc/terms/title.

3. Basic Concepts

This section is non-normative.

JSON [RFC8259] is a lightweight, language-independent data interchange format.
It is easy to parse and easy to generate. However, it is difficult to integrate JSON
from different sources as the data may contain keys that conflict with other
data sources. Furthermore, JSON has no
built-in support for hyperlinks, which are a fundamental building block on
the Web. Let's start by looking at an example that we will be using for the
rest of this section:

It's obvious to humans that the data is about a person whose
name is "Manu Sporny"
and that the homepage property contains the URL of that person's homepage.
A machine doesn't have such an intuitive understanding and sometimes,
even for humans, it is difficult to resolve ambiguities in such representations. This problem
can be solved by using unambiguous identifiers to denote the different concepts instead of
tokens such as "name", "homepage", etc.

Linked Data, and the Web in general, uses IRIs
(Internationalized Resource Identifiers as described in [RFC3987]) for unambiguous
identification. The idea is to use IRIs
to assign unambiguous identifiers to data that may be of use to other developers.
It is useful for terms,
like name and homepage, to expand to IRIs
so that developers don't accidentally step on each other's terms. Furthermore, developers and
machines are able to use this IRI (by using a web browser, for instance) to go to
the term and get a definition of what the term means. This process is known as IRI
dereferencing.

Leveraging the popular schema.org vocabulary,
the example above could be unambiguously expressed as follows:

In the example above, every property is unambiguously identified by an IRI and all values
representing IRIs are explicitly marked as such by the
@idkeyword. While this is a valid JSON-LD
document that is very specific about its data, the document is also overly verbose and difficult
to work with for human developers. To address this issue, JSON-LD introduces the notion
of a context as described in the next section.

3.1 The Context

This section is non-normative.

When two people communicate with one another, the conversation takes
place in a shared environment, typically called
"the context of the conversation". This shared context allows the
individuals to use shortcut terms, like the first name of a mutual friend,
to communicate more quickly but without losing accuracy. A context in
JSON-LD works in the same way. It allows two applications to use shortcut
terms to communicate with one another more efficiently, but without
losing accuracy.

Simply speaking, a context is used to map terms to IRIs.
Terms are case sensitive and most valid strings that are not reserved JSON-LD keywords
can be used as a term.
Exceptions are the empty string "" and strings that have the form
of a keyword (i.e., starting with "@" followed exclusively by one or more ALPHA characters (see [RFC5234])), which must not be used as terms.
Strings that have the form of
an IRI (e.g., containing a ":") should not be used as terms.

For the sample document in the previous section, a context would
look something like this:

{
"@context": {
"name": "http://schema.org/name",↑ This means that 'name' is shorthand for 'http://schema.org/name'"image": {
"@id": "http://schema.org/image",↑ This means that 'image' is shorthand for 'http://schema.org/image'"@type": "@id"↑ This means that a string value associated with 'image'
should be interpreted as an identifier that is an IRI},
"homepage": {
"@id": "http://schema.org/url",↑ This means that 'homepage' is shorthand for 'http://schema.org/url'"@type": "@id"↑ This means that a string value associated with 'homepage'
should be interpreted as an identifier that is an IRI
}
}
}

Contexts can either be directly embedded
into the document (an embedded context) or be referenced using a URL.
Assuming the context document in the previous
example can be retrieved at https://json-ld.org/contexts/person.jsonld,
it can be referenced by adding a single line and allows a JSON-LD document to
be expressed much more concisely as shown in the example below:

The referenced context not only specifies how the terms map to
IRIs in the Schema.org vocabulary but also
specifies that string values associated with
the homepage and image property
can be interpreted as an IRI ("@type": "@id",
see § 3.2 IRIs for more details). This information allows developers
to re-use each other's data without having to agree to how their data will interoperate
on a site-by-site basis. External JSON-LD context documents may contain extra
information located outside of the @context key, such as
documentation about the terms declared in the
document. Information contained outside of the @context value
is ignored when the document is used as an external JSON-LD context document.

A remote context may also be referenced using a relative URL,
which is resolved relative to the location of the document containing the reference.
For example, if a document were located at http://example.org/document.jsonld
and contained a relative reference to context.jsonld,
the referenced context document would be found relative at http://example.org/context.jsonld.

As noted in § 1.1 How to Read this Document,
IRIs can often be confused with URLs (Uniform Resource Locators),
the primary distinction is that a URL locates a resource on the web,
an IRIidentifies a resource. While it is a good practice for resource identifiers
to be dereferenceable, sometimes this is not practical. In particular, note the
[URN] scheme for Uniform Resource Names, such as UUID.
An example UUID is urn:uuid:f81d4fae-7dec-11d0-a765-00a0c91e6bf6.

In the example above, since the value http://manu.sporny.org/
is expressed as a JSON string, the type coercion
rules will transform the value into an IRI when processing the data.
See § 4.2.3 Type Coercion for more
details about this feature.

In summary, IRIs can be expressed in a variety of
different ways in JSON-LD:

An IRI is generated for the string value specified using
@id or @type.

An IRI is generated for the string value of any key for which there
are coercion rules that contain an @type key that is
set to a value of @id or @vocab.

This section only covers the most basic features associated with IRIs
in JSON-LD. More advanced features related to IRIs are covered in
section § 4. Advanced Concepts.

3.3 Node Identifiers

This section is non-normative.

To be able to externally reference nodes
in an RDF graph, it is important that
nodes have an identifier. IRIs
are a fundamental concept of Linked Data, for
nodes to be truly linked, dereferencing the
identifier should result in a representation of that node.
This may allow an application to retrieve further information about a
node.

The JSON-LD data model allows for a richer set of resources, based on the RDF data model.
The data model is described more fully in § 8. Data Model.
JSON-LD uses JSON objects to describe various resources, along with the relationships
between these resources:

3.5 Specifying the Type

This section is non-normative.

In Linked Data, it is common to specify the type of a graph node;
in many cases, this can be inferred based on the properties used within a
given node object, or the property for which a node is a value. For
example, in the schema.org vocabulary, the givenName
property is associated with a Person. Therefore, one may reason that
if a node object contains the property givenName, that the
type is a Person; making this explicit with @type helps
to clarify the association.

The type of a particular node can be specified using the @typekeyword. In Linked Data, types are uniquely
identified with an IRI.

In addition to setting the type of nodes,
@type can also be used to set the type of a value
to create a typed value.
This use of @type is similar to that used to define the type of a node object,
but value objects are restricted to having just a single type.
The use of @type to create typed values is discussed more fully in § 4.2.1 Typed Values.

Typed values can also be defined implicitly, by specifying
@type in an expanded term definition.
This is covered more fully in § 4.2.3 Type Coercion.

4. Advanced Concepts

This section is non-normative.

JSON-LD has a number of features that provide functionality above and beyond
the core functionality described above. JSON can be used to express data
using such structures, and the features described in this
section can be used to interpret a variety of different JSON structures as
Linked Data. A JSON-LD processor will make use of provided and embedded
contexts to interpret property values in a number of different idiomatic
ways.

Describing values

One pattern in JSON is for the value of a property to be a string.
Often times, this string actually represents some other typed value, for
example an IRI, a date, or a string in some specific language. See § 4.2 Describing Values for details on how to
describe such value typing.

Value ordering

In JSON, a property with an array value implies an implicit order;
arrays in JSON-LD do not convey any ordering of the contained elements by
default, unless defined using embedded structures or through a context
definition. See § 4.3 Value Ordering for a
further discussion.

Property nesting

Another JSON idiom often found in APIs is to use an
intermediate object to group together related properties of an object; in JSON-LD
these are referred to as nested properties and are described in § 4.4 Nested Properties.

Referencing objects

Linked Data is all about describing the relationships between different resources.
Sometimes these relationships are between resources defined in different
documents described on the web, sometimes the resources are described
within the same document.

In this case, a document residing at http://manu.sporny.org/about
may contain the example above, and reference another document at
https://greggkellogg.net/foaf which could include a similar
representation.

A common idiom found in JSON usage is objects being specified as the
value of other objects, called object embedding in JSON-LD;
for example, a friend specified as an
object value of a Person:

Another common idiom in JSON is to use an intermediate object to represent property values via indexing. JSON-LD allows data to be indexed
in a number of different ways, as detailed in § 4.6 Indexed Values.

The following sections describe such
advanced functionality in more detail.

4.1 Advanced Context Usage

This section is non-normative.

Section § 3.1 The Context introduced the basics of what makes
JSON-LD work. This section expands on the basic principles of the
context and demonstrates how more advanced use cases can
be achieved using JSON-LD.

In general, contexts may be used any time a
map is defined.
The only time that one cannot express a context is as a direct child of another context definition (other than as part of an expanded term definition).
For example, a JSON-LD document may
have the form of an array composed of one or more node objects,
which use a context definition in each top-level node object:

The outer array is standard for a document in
expanded document form
and flattened document form,
and may be necessary when describing a disconnected graph,
where nodes may not reference each other. In such cases, using
a top-level map with a @graph property can be useful for saving
the repetition of @context. See § 4.5 Embedding
for more.

In the example above, the nameterm is overridden
in the more deeply nested details structure,
which uses its own embedded context.
Note that this is
rarely a good authoring practice and is typically used when working with
legacy applications that depend on a specific structure of the
map. If a term is redefined within a
context, all previous rules associated with the previous definition are
removed. If a term is redefined to null,
the term is effectively removed from the list of
terms defined in the active context.

When possible, the context definition should be put
at the top of a JSON-LD document. This makes the document easier to read and
might make streaming parsers more efficient. Documents that do not have the
context at the top are still conformant JSON-LD.

Note

To avoid forward-compatibility issues, terms
starting with an @ character
followed exclusively by one or more ALPHA characters (see [RFC5234])
are to be avoided as they
might be used as keyword in future versions
of JSON-LD. Terms starting with an @ character that are not
JSON-LD 1.1 keywords are treated as any other term, i.e.,
they are ignored unless mapped to an IRI. Furthermore, the use of
empty terms ("") is not allowed as
not all programming languages are able to handle empty JSON keys.

4.1.1 JSON-LD 1.1 Processing Mode

This section is non-normative.

New features defined in JSON-LD 1.1 are available
unless the processing mode is set to json-ld-1.0.
This may be set through an API option.
The processing mode may be explicitly set to json-ld-1.1 using the @versionentry in a context
set to the value 1.1 as a number, or through an API option.
Explicitly setting the processing mode to json-ld-1.1
will prohibit JSON-LD 1.0 processors from incorrectly processing a JSON-LD 1.1 document.

The first context encountered when processing a
document which contains @version determines the processing mode,
unless it is defined explicitly through an API option.
This means that if "@version": 1.1 is encountered after processing a context
without @version,
the former will be interpreted as having had "@version": 1.1 defined within it.

Note

Setting the processing mode explicitly
to json-ld-1.1 is RECOMMENDED to prevent a JSON-LD 1.0 processor
from incorrectly processing a JSON-LD 1.1 document and
producing different results.

4.1.2 Default Vocabulary

This section is non-normative.

At times, all properties and types may come from the same vocabulary. JSON-LD's
@vocab keyword allows an author to set a common prefix which
is used as the vocabulary mapping and is used
for all properties and types that do not match a term and are neither
an IRI nor a compact IRI (i.e., they do
not contain a colon).

If @vocab is used but certain keys in an
map should not be expanded using
the vocabulary IRI, a term can be explicitly set
to null in the context. For instance, in the
example below the databaseIdentry would not expand to an
IRI causing the property to be dropped when expanding.

The grammar for @vocab, as defined in § 9.15 Context Definitions
allows the value to be a term or compact IRI.
Note that terms used in the value of @vocab must be in scope at the time the context is introduced,
otherwise there would be a circular dependency between @vocab and other terms defined in the same context.

This document uses an empty @id, which resolves to the document base.
However, if the document is moved to a different location, the IRI would change.
To prevent this without having to use an IRI, a context
may define an @base mapping, to overwrite the base IRI for the document.

Please note that the @base will be ignored if used in
external contexts.

4.1.4 Using the Document Base for the Default Vocabulary

This section is non-normative.

In some cases, vocabulary terms are defined directly within the document
itself, rather than in an external vocabulary.
Since JSON-LD 1.1, the vocabulary mapping in a local context
can be set to a relative IRI reference,
which is, if there is no vocabulary mapping in scope, resolved against the base IRI.
This causes terms which are expanded relative to the vocabulary,
such as the keys of node objects,
to be based on the base IRI to create IRIs.

4.1.5 Compact IRIs

This section is non-normative.

A compact IRI is a way of expressing an IRI
using a prefix and suffix separated by a colon (:).
The prefix is a term taken from the
active context and is a short string identifying a
particular IRI in a JSON-LD document. For example, the
prefix foaf may be used as a shorthand for the
Friend-of-a-Friend vocabulary, which is identified using the IRIhttp://xmlns.com/foaf/0.1/. A developer may append
any of the FOAF vocabulary terms to the end of the prefix to specify a short-hand
version of the IRI for the vocabulary term. For example,
foaf:name would be expanded to the IRIhttp://xmlns.com/foaf/0.1/name.

In the example above, foaf:name expands to the IRIhttp://xmlns.com/foaf/0.1/name and foaf:Person expands
to http://xmlns.com/foaf/0.1/Person.

Prefixes are expanded when the form of the value
is a compact IRI represented as a prefix:suffix
combination, the prefix matches a term defined within the
active context, and the suffix does not begin with two
slashes (//). The compact IRI is expanded by
concatenating the IRI mapped to the prefix to the (possibly empty)
suffix. If the prefix is not defined in the active context,
or the suffix begins with two slashes (such as in http://example.com),
the value is interpreted as IRI instead. If the prefix is an
underscore (_), the value is interpreted as blank node identifier
instead.

It's also possible to use compact IRIs within the context as shown in the
following example:

The term selection behavior for 1.0 processors was changed
as a result of an errata against JSON-LD 1.0 reported here.
This does not affect the behavior of processing existing JSON-LD documents, but creates
a slight change when compacting documents using Compact IRIs.

The behavior when compacting can be illustrated by considering the following input
document in expanded form:

In this case, the property term would not normally be usable as a prefix, both
because it is defined with an expanded term definition, and because
its @id does not end in a
gen-delim character. Adding
"@prefix": true allows it to be used as the prefix portion of
the compact IRIproperty:One.

4.1.6 Aliasing Keywords

This section is non-normative.

Each of the JSON-LD keywords,
except for @context, may be aliased to application-specific
keywords. This feature allows legacy JSON content to be utilized
by JSON-LD by re-using JSON keys that already exist in legacy documents.
This feature also allows developers to design domain-specific implementations
using only the JSON-LD context.

4.1.7 IRI Expansion within a Context

This section is non-normative.

In general, normal IRI expansion rules apply
anywhere an IRI is expected (see § 3.2 IRIs). Within
a context definition, this can mean that terms defined
within the context may also be used within that context as long as
there are no circular dependencies. For example, it is common to use
the xsd namespace when defining typed values:

In this example, the compact IRI form is used in two different ways.
In the first approach, foaf:age declares both the
IRI for the term (using short-form) as well as the
@type associated with the term. In the second
approach, only the @type associated with the term is
specified. The full IRI for
foaf:homepage is determined by looking up the foafprefix in the
context.

Warning

If a compact IRI is used as a term, it must expand to the
value that compact IRI would have on its own when expanded.
This represents a change to the original 1.0 algorithm to prevent terms from
expanding to a different IRI, which could lead to undesired results.

In order for the IRI to match above, the IRI
needs to be used in the JSON-LD document. Also note that foaf:homepage
will not use the { "@type": "@id" } declaration because
foaf:homepage is not the same as http://xmlns.com/foaf/0.1/homepage.
That is, terms are looked up in a context using
direct string comparison before the prefix lookup mechanism is applied.

Warning

Neither an IRI reference nor a compact IRI
may expand to some other unrelated IRI.
This represents a change to the original 1.0 algorithm which allowed this behavior but discouraged it.

The only other exception for using terms in the context is that
circular definitions are not allowed. That is,
a definition of term1 cannot depend on the
definition of term2 if term2 also depends on
term1. For example, the following context definition
is illegal:

In this case, the social profile is defined using the schema.org vocabulary,
but interest is imported from FOAF,
and is used to define a node describing one of Manu's interests
where those properties now come from the FOAF vocabulary.

Expanding this document, uses a combination of terms defined in the outer context,
and those defined specifically for that term in a property-scoped context.

Scoping can also be performed using a term used as a value of @type:

Example 46: Defining an @context within a term definition used on @type

Scoping on @type is useful when common properties are used to
relate things of different types, where the vocabularies in use within
different entities calls for different context scoping. For example,
hasPart/partOf may be common terms used in a document, but mean
different things depending on the context.
A type-scoped context is only in effect for the node object on which
the type is used; the previous in-scope contexts are placed back into
effect when traversing into another node object.
As described further in § 4.1.9 Context Propagation,
this may be controlled using the @propagate keyword.

4.1.9 Context Propagation

This section is non-normative.

Once introduced, contexts remain in effect until a subsequent
context removes it by setting @context to null,
or by redefining terms,
with the exception of type-scoped contexts,
which limit the effect of that context until the next node object is entered.
This behavior can be changed using the @propagate keyword.

The following example illustrates how terms defined in a context with @propagate set to false
are effectively removed when descending into new node object.

{
"@context": {
"@version": 1.1,
"term": {
"@id": "http://example.org/original",
"@context": {
"@propagate": false,
↑ Scoped context only lasts in one node-object
"term": "http://example.org/non-propagated-term"
}
}
},
"term": {
↑ This term is the original
"term": {
↑ This term is from the scoped context
"term": "This term is from the first context"
↑ This term is the original again
}
}
}

4.1.10 Imported Contexts

JSON-LD 1.0 included mechanisms for modifying the context that
is in effect. This included the capability to load and process a remote
context and then apply further changes to it via new contexts.

However, with the introduction of JSON-LD 1.1, it is also desirable to
be able to load a remote context, in particular an existing JSON-LD
1.0 context, and apply JSON-LD 1.1 features to it prior to
processing.

By using the @import keyword in a context, another remote
context, referred to as an imported context, can be loaded and
modified prior to processing. The modifications are expressed in the
context that includes the @import keyword, referred to as the
wrapping context. Once an imported context is loaded, the
contents of the wrapping context are merged into it prior to
processing. The merge operation will cause each key-value pair in the
wrapping context to be added to the loaded imported context,
with the wrapping context key-value pairs taking precedence.

By enabling existing contexts to be reused and edited inline prior
to processing, context-wide keywords can be applied to adjust all term
definitions in the imported context. Similarly, term definitions can
be replaced prior to processing, enabling adjustments that, for instance, ensure term
definitions match previously protected terms or that they include
additional type coercion information.

The following examples illustrate how @import can be used to express
a type-scoped context that loads an imported context and
sets @propagate to true, as a technique for making other similar modifications.

Suppose there was a context that could be referenced remotely
via the URL https://json-ld.org/contexts/remote-context.jsonld:

4.1.11 Protected Term Definitions

This section is non-normative.

JSON-LD is used in many specifications as the specified data format.
However, there is also a desire to allow some JSON-LD contents to be processed as plain JSON,
without using any of the JSON-LD algorithms.
Because JSON-LD is very flexible,
some terms from the original format may be locally overridden
through the use of embedded contexts,
and take a different meaning for JSON-LD based implementations.
On the other hand, "plain JSON" implementations may not be able to interpret these embedded contexts,
and hence will still interpret those terms with their original meaning.
To prevent this divergence of interpretation,
JSON-LD 1.1 allows term definitions to be protected.

A protected term definition is a term definition with an entry@protected set to true.
It generally prevents further contexts from overriding this term definition,
either through a new definition of the same term,
or through clearing the context with "@context": null.
Such attempts will raise an error and abort the processing
(except in some specific situations described
below).

Example 55: A protected term definition can generally not be overridden

When all or most term definitions of a context need to be protected,
it is possible to add an entry@protected set to true
to the context itself.
It has the same effect as protecting each of its term definitions individually.
Exceptions can be made by adding an entry@protected set to false
in some term definitions.

While protected terms can in general not be overridden,
there are two exceptions to this rule.
The first exception is that a context is allowed to redefine a protected term
if the new definition is identical to the protected term definition
(modulo the @protected flag).
The rationale is that the new definition does not violate the protection,
as it does not change the semantics of the protected term.
This is useful for widespread term definitions,
such as aliasing @type to type,
which may occur (including in a protected form) in several contexts.

The second exception is that a property-scoped context
is not affected by protection, and can therefore override protected terms,
either with a new term definition,
or by clearing the context with "@context": null.

The rationale is that "plain JSON" implementations,
relying on a given specification,
will only traverse properties defined by that specification.
Scoped contexts belonging to the specified properties are part of the specification,
so the "plain JSON" implementations are expected to be aware of the change of semantics they induce.
Scoped contexts belonging to other properties apply to parts of the document that "plain JSON" implementations will ignore.
In both cases, there is therefore no risk of diverging interpretations between JSON-LD-aware implementations and "plain JSON" implementations,
so overriding is permitted.

By preventing terms from being overridden,
protection also prevents any adaptation of a term
(e.g., defining a more precise datatype, restricting the term's use to lists, etc.).
This kind of adaptation is frequent with some general purpose contexts,
for which protection would therefore hinder their usability.
As a consequence, context publishers should use this feature with care.

Note

Protected term definitions are a new feature in JSON-LD 1.1.

4.2 Describing Values

This section is non-normative.

Values are leaf nodes in a graph associated with scalar values such as
strings, dates, times, and other such atomic values.

4.2.1 Typed Values

This section is non-normative.

A value with an associated type, also known as a
typed value, is indicated by associating a value with
an IRI which indicates the value's type. Typed values may be
expressed in JSON-LD in three ways:

By utilizing the @typekeyword when defining
a term within an @context section.

The modified key's value above is automatically interpreted as a
dateTime value because of the information specified in the
@context. The example tabs show how a JSON-LD processor will interpret the data.

The second example uses the expanded form of setting the type information
in the body of a JSON-LD document:

Both examples above would generate the value
2010-05-29T14:17:39+02:00 with the type
http://www.w3.org/2001/XMLSchema#dateTime. Note that it is
also possible to use a term or a compact IRI to
express the value of a type.

A node type specifies the type of thing
that is being described, like a person, place, event, or web page. A
value type specifies the data type of a particular value, such
as an integer, a floating point number, or a date.

The first use of @type associates a node type
(http://schema.org/BlogPosting) with the node,
which is expressed using the @idkeyword.
The second use of @type associates a value type
(http://www.w3.org/2001/XMLSchema#dateTime) with the
value expressed using the @valuekeyword. As a
general rule, when @value and @type are used in
the same map, the @typekeyword is expressing a value type.
Otherwise, the @typekeyword is expressing a
node type. The example above expresses the following data:

4.2.2 JSON Literals

This section is non-normative.

At times, it is useful to include JSON within JSON-LD that is not interpreted as JSON-LD.
Generally, a JSON-LD processor will ignore properties which don't map to IRIs,
but this causes them to be excluded when performing various algorithmic transformations.
But, when the data that is being described is, itself, JSON, it's important that
it survive algorithmic transformations.

Warning

JSON-LD is intended to allow native JSON to be
interpreted through the use of a context.
The use of JSON literals creates blobs of data which are not available for interpretation.
It is for use only in the rare cases that JSON cannot be represented as JSON-LD.

When a term is defined with @type set to @json,
a JSON-LD processor will treat the value as a JSON literal,
rather than interpreting it further as JSON-LD.
In the expanded document form, such JSON will become the value of @value within a value object
having "@type": "@json".

The following example shows an example of a JSON Literal contained as the
value of a property. Note that the RDF results use a canonicalized form of the JSON
to ensure interoperability between different processors.
JSON canonicalization is described in Data Round Tripping in [JSON-LD11-API].

Generally, when a JSON-LD processor encounters null,
the associated entry or value is removed.
However, null is a valid JSON token; when used as the value
of a JSON literal, a null value will be preserved.

4.2.3 Type Coercion

This section is non-normative.

JSON-LD supports the coercion of string values to particular data types.
Type coercion allows someone deploying JSON-LD to use string property values
and have those values be interpreted as typed values
by associating an IRI with the value in the expanded value object representation.
Using type coercion, string value representation can be used without requiring
the data type to be specified explicitly with each piece of data.

Type coercion is specified within an expanded term definition
using the @type key. The value of this key expands to an IRI.
Alternatively, the keyword@id or @vocab may be used
as value to indicate that within the body of a JSON-LD document, a string value of a
term coerced to @id or @vocab is to be interpreted as an
IRI. The difference between @id and @vocab is how values are expanded
to IRIs. @vocab first tries to expand the value
by interpreting it as term. If no matching term is found in the
active context, it tries to expand it as an IRI or a compact IRI
if there's a colon in the value; otherwise, it will expand the value using the
active context'svocabulary mapping, if present.
Values coerced to @id in contrast are expanded as
an IRI or a compact IRI if a colon is present; otherwise, they are interpreted
as relative IRI references.

Note

The ability to coerce a value using a term definition is distinct
from setting one or more types on a node object, as the former does not result in
new data being added to the graph, while the later manages node types
through adding additional relationships to the graph.

Terms or compact IRIs used as the value of a
@type key may be defined within the same context. This means that one may specify a
term like xsd and then use xsd:integer within the same
context definition.

The example below demonstrates how a JSON-LD author can coerce values to
typed values and IRIs.

It is important to note that terms are only used in expansion
for vocabulary-relative positions, such as for keys and values of map entries.
Values of @id are considered to be document-relative,
and do not use term definitions for expansion. For example, consider the following:

The unexpected result is that "barney" expands to both http://example1.com/barney
and http://example2.com/barney, depending where it is encountered.
String values interpreted as IRIs because of the associated term definitions
are typically considered to be document-relative.
In some cases, it makes sense to interpret these relative to the vocabulary,
prescribed using "@type": "@vocab" in the term definition, though this can
lead to unexpected consequences such as these.

In the previous example, "barney" appears twice, once as the value of @id,
which is always interpreted as a document-relative IRI, and once as the value of
"fred", which is defined to be vocabulary-relative, thus the different expanded values.

In this case the @id definition in the term definition is optional.
If it does exist, the IRI or compact IRI representing
the term will always be expanded to IRI defined by the @id
key—regardless of whether a prefix is defined or not.

Type coercion is always performed using the unexpanded value of the key. In the
example above, that means that type coercion is done looking for foaf:age
in the active context and not for the corresponding, expanded
IRIhttp://xmlns.com/foaf/0.1/age.

Note

Keys in the context are treated as terms for the purpose of
expansion and value coercion. At times, this may result in multiple representations for the same expanded IRI.
For example, one could specify that dog and cat both expanded to http://example.com/vocab#animal.
Doing this could be useful for establishing different type coercion or language specification rules.

4.2.4 String Internationalization

This section is non-normative.

At times, it is important to annotate a string
with its language. In JSON-LD this is possible in a variety of ways.
First, it is possible to define a default language for a JSON-LD document
by setting the @language key in the context:

The example above would associate 忍者 with the specified default
language tag ja, Ninja with the language tag
en, and Nindža with the language tag cs.
The value of name, Yagyū Muneyoshi wouldn't be
associated with any language tag since @language was reset to
null in the expanded term definition.

Just as in the example above, systems often need to express the value of a
property in multiple languages. Typically, such systems also try to ensure that
developers have a programmatically easy way to navigate the data structures for
the language-specific data. In this case, language maps
may be utilized.

The example above expresses exactly the same information as the previous
example but consolidates all values in a single property. To access the
value in a specific language in a programming language supporting dot-notation
accessors for object properties, a developer may use the
property.language pattern
(when languages are limited to the primary language sub-tag,
and do not depend on other sub-tags, such as "en-us").
For example, to access the occupation
in English, a developer would use the following code snippet:
obj.occupation.en.

4.3 Value Ordering

This section is non-normative.

A JSON-LD author can express multiple values in a compact way by using
arrays. Since graphs do not describe ordering for links
between nodes, arrays in JSON-LD do not convey any ordering of the
contained elements by default. This is exactly the opposite from regular JSON
arrays, which are ordered by default. For example, consider the following
simple document:

This describes the use of this array as being ordered,
and order is maintained when processing a document. If every use of a given multi-valued
property is a list, this may be abbreviated by setting @container
to @list in the context:

The implementation of lists in RDF depends on linking anonymous nodes
together using the properties rdf:first and
rdf:rest, with the end of the list defined as the resource
rdf:nil, as the "statements" tab illustrates.
This allows order to be represented within an unordered set of statements.

Both JSON-LD and Turtle provide shortcuts for representing ordered lists.

In JSON-LD 1.1, lists of lists, where the value of
a list object, may itself be a list object, are
fully supported.

Note that the "@container": "@list" definition recursively
describes array values of lists as being, themselves, lists. For example, in The GeoJSON Format (see [RFC7946]),
coordinates are an ordered list of positions, which are
represented as an array of two or more numbers:

For these examples, it's important that values
expressed within bbox and coordinates maintain their order,
which requires the use of embedded list structures. In JSON-LD 1.1, we can
express this using recursive lists, by simply adding the appropriate context
definition:

Values of terms associated with an @list container
are always represented in the form of an array,
even if there is just a single value or no value at all.

4.3.2 Sets

This section is non-normative.

While @list is used to describe ordered lists,
the @set keyword is used to describe unordered sets.
The use of @set in the body of a JSON-LD document
is optimized away when processing the document, as it is just syntactic
sugar. However, @set is helpful when used within the context
of a document.
Values of terms associated with an @set container
are always represented in the form of an array,
even if there is just a single value that would otherwise be optimized to
a non-array form in compact form (see
§ 5.2 Compacted Document Form). This makes post-processing of
JSON-LD documents easier as the data is always in array form, even if the
array only contains a single value.

This describes the use of this array as being unordered,
and order may change when processing a document. By default,
arrays of values are unordered, but this may be made explicit by
setting @container to @set in the context:

Since JSON-LD 1.1, the @set keyword may be
combined with other container specifications within an expanded term
definition to similarly cause compacted values of indexes to be consistently
represented using arrays. See § 4.6 Indexed Values for a further discussion.

4.4 Nested Properties

This section is non-normative.

Many JSON APIs separate properties from their entities using an
intermediate object; in JSON-LD these are called nested properties.
For example, a set of possible labels may be grouped
under a common property:

By defining labels using the keyword@nest,
a JSON-LD processor will ignore the nesting created by using the
labels property and process the contents as if it were declared
directly within containing object. In this case, the labels
property is semantically meaningless. Defining it as equivalent to
@nest causes it to be ignored when expanding, making it
equivalent to the following:

Similarly, term definitions may contain a @nest property
referencing a term aliased to @nest which will cause such
properties to be nested under that aliased term when compacting.
In the example below, both main_label and other_label are defined
with "@nest": "labels", which will cause them to be serialized under
labels when compacting.

The previous example describes two node objects, for Manu and Gregg, with
the knows property defined to treat string values as identifiers.
Embedding allows the node object for Gregg to be embedded as a value
of the knows property:

Example 94: Embedding a node object as property value of another node object

A node object, like the one used above, may be used in
any value position in the body of a JSON-LD document.

While it is considered a best practice to identify nodes in a graph,
at times this is impractical. In the data model, nodes without an explicit
identifier are called blank nodes, which can be represented in a
serialization such as JSON-LD using a blank node identifier. In the
previous example, the top-level node for Manu does not have an identifier,
and does not need one to describe it within the data model. However, if we
were to want to describe a knows relationship from Gregg to Manu,
we would need to introduce a blank node identifier
(here _:b0).

Blank node identifiers may be automatically introduced by algorithms such as flattening, but they are also useful for authors to describe such relationships directly.

4.5.1 Identifying Blank Nodes

This section is non-normative.

At times, it becomes necessary to be able to express information without
being able to uniquely identify the node with an IRI.
This type of node is called a blank node. JSON-LD does not require
all nodes to be identified using @id. However, some graph topologies
may require identifiers to be serializable. Graphs containing loops, e.g., cannot
be serialized using embedding alone, @id must be used to connect the nodes.
In these situations, one can use blank node identifiers,
which look like IRIs using an underscore (_)
as scheme. This allows one to reference the node locally within the document, but
makes it impossible to reference the node from an external document. The
blank node identifier is scoped to the document in which it is used.

The example above contains information about two secret agents that cannot be identified
with an IRI. While expressing that agent 1 knows agent 2
is possible without using blank node identifiers,
it is necessary to assign agent 1 an identifier so that it can be referenced
from agent 2.

It is worth noting that blank node identifiers may be relabeled during processing.
If a developer finds that they refer to the blank node more than once,
they should consider naming the node using a dereferenceable IRI so that
it can also be referenced from other documents.

4.6 Indexed Values

This section is non-normative.

Sometimes multiple property values need to be accessed
in a more direct fashion than iterating though multiple array values. JSON-LD
provides an indexing mechanism to allow the use of an intermediate map
to associate specific indexes with associated values.

4.6.1 Data Indexing

This section is non-normative.

Databases are typically used to make access to
data more efficient. Developers often extend this sort of functionality into
their application data to deliver similar performance gains.
This data may have no meaning from a Linked Data standpoint, but is
still useful for an application.

JSON-LD introduces the notion of index maps
that can be used to structure data into a form that is
more efficient to access. The data indexing feature allows an author to
structure data using a simple key-value map where the keys do not map
to IRIs. This enables direct access to data
instead of having to scan an array in search of a specific item.
In JSON-LD such data can be specified by associating the
@indexkeyword with a
@container declaration in the context:

In the example above, the athletesterm has
been marked as an index map.
The catcher and pitcher keys will be ignored semantically,
but preserved syntactically, by the JSON-LD Processor.
If used in JavaScript, this can allow a developer to access a particular athlete using the
following code snippet: obj.athletes.pitcher.

4.6.1.1 Property-based data indexing

This section is non-normative.

In its simplest form (as in the examples above),
data indexing assigns no semantics to the keys of an index map.
However, in some situations,
the keys used to index objects are semantically linked to these objects,
and should be preserved not only syntactically, but also semantically.

Unless the processing mode is set to json-ld-1.0,
"@container": "@index" in a term description can be accompanied with
an "@index" key. The value of that key must map to an IRI,
which identifies the semantic property linking each object to its key.

4.6.2 Language Indexing

This section is non-normative.

JSON which includes string values in multiple languages may be
represented using a language map to allow for easily
indexing property values by language tag. This enables direct access to
language values instead of having to scan an array in search of a specific item.
In JSON-LD such data can be specified by associating the
@languagekeyword with a
@container declaration in the context:

In the example above, the labelterm has
been marked as a language map. The en and
de keys are implicitly associated with their respective
values by the JSON-LD Processor. This allows a developer to
access the German version of the label using the
following code snippet: obj.label.de,
which, again, is only appropriate when languages are limited to the
primary language sub-tag and do not depend on other sub-tags, such as "de-at".

The value of @container can also
be an array containing both @language and @set.
When compacting, this ensures that a JSON-LD Processor will use
the array form for all values of language tags.

Unless the processing mode is set to json-ld-1.0,
the special index @none is used for indexing
strings which do not have a language; this is useful to maintain
a normalized representation for string values not having a datatype.

Example 102: Indexing languaged-tagged strings using @none for no language

4.6.3 Node Identifier Indexing

This section is non-normative.

In addition to index maps, JSON-LD introduces the notion of id maps
for structuring data. The id indexing feature allows an author to
structure data using a simple key-value map where the keys map
to IRIs. This enables direct access to associated node objects
instead of having to scan an array in search of a specific item.
In JSON-LD such data can be specified by associating the
@idkeyword with a
@container declaration in the context:

In the example above, the postterm has
been marked as an id map. The http://example.com/posts/1/en and
http://example.com/posts/1/de keys will be interpreted
as the @id property of the node object value.

The special index @none is used for indexing
node objects which do not have an @id, which is useful to maintain
a normalized representation. The @none index may also be
a term which expands to @none, such as the term none
used in the example below.

4.6.4 Node Type Indexing

This section is non-normative.

In addition to id and index maps, JSON-LD introduces the notion of type maps
for structuring data. The type indexing feature allows an author to
structure data using a simple key-value map where the keys map
to IRIs. This enables data to be structured based on the @type
of specific node objects.
In JSON-LD such data can be specified by associating the
@typekeyword with a
@container declaration in the context:

The special index @none is used for indexing
node objects which do not have an @type, which is useful to maintain
a normalized representation. The @none index may also be
a term which expands to @none, such as the term none
used in the example below.

4.7 Included Nodes

This section is non-normative.

Sometimes it is also useful to list node objects as part of another node object.
For instance, to represent a set of resources which are used by some other
resource. Included blocks may be also be used to collect such secondary node objects
which can be referenced from a primary node object.
For an example, consider a node object containing a list of different items,
some of which share some common elements:

However, in contrast to @graph, @included does not interact with other properties
contained within the same map, a feature discussed further in § 4.9 Named Graphs.

4.8 Reverse Properties

This section is non-normative.

JSON-LD serializes directed graphs. That means that
every property points from a node to another node
or value. However, in some cases, it is desirable
to serialize in the reverse direction. Consider for example the case where a person
and its children should be described in a document. If the used vocabulary does not
provide a childrenproperty but just a parentproperty, every node representing a child would have to
be expressed with a property pointing to the parent as in the following
example.

4.9 Named Graphs

This section is non-normative.

At times, it is necessary to make statements about a graph
itself, rather than just a single node. This can be done by
grouping a set of nodes using the @graphkeyword. A developer may also name data expressed using the
@graphkeyword by pairing it with an
@idkeyword as shown in the following example:

The example above expresses a named graph that is identified
by the IRIhttp://example.org/foaf-graph. That
graph is composed of the statements about Manu and Gregg. Metadata about
the graph itself is expressed via the generatedAt property,
which specifies when the graph was generated.

When a JSON-LD document's top-level structure is a
map that contains no other
keys than @graph and
optionally @context (properties that are not mapped to an
IRI or a keyword are ignored),
@graph is considered to express the otherwise implicit
default graph. This mechanism can be useful when a number
of nodes exist at the document's top level that
share the same context, which is, e.g., the case when a
document is flattened. The
@graph keyword collects such nodes in an array
and allows the use of a shared context.

4.9.1 Graph Containers

This section is non-normative.

In some cases, it is useful to logically partition data into separate
graphs, without making this explicit within the JSON expression. For
example, a JSON document may contain data against which other metadata is
asserted and it is useful to separate this data in the data model using
the notion of named graphs, without the syntactic overhead
associated with the @graph keyword.

The example above expresses an anonymously named graph
making a statement. The default graph includes a statement
saying that the subject wrote that statement.
This is an example of separating statements into a named graph, and then
making assertions about the statements contained within that named graph.

4.9.2 Named Graph Data Indexing

This section is non-normative.

In addition to indexing node objects by index, graph objects may
also be indexed by an index. By using the @graph
container type, introduced in § 4.9.1 Graph Containers
in addition to @index, an object value of such a property is
treated as a key-value map where the keys do not map to IRIs, but
are taken from an @index property associated with named graphs
which are their values. When expanded, these must be simple graph objects

As with index maps, when used with @graph, a container may also
include @set to ensure that key values are always contained in an array.

The special index @none is used for indexing
graphs which do not have an @index key, which is useful to maintain
a normalized representation. Note, however, that
compacting a document where multiple unidentified named graphs are
compacted using the @none index will result in the content
of those graphs being merged. To prevent this, give each graph a distinct
@index key.

As with id maps, when used with @graph, a container may also
include @set to ensure that key values are always contained in an array.

As with id maps, the special index @none is used for indexing
named graphs which do not have an @id, which is useful to maintain
a normalized representation. The @none index may also be
a term which expands to @none.
Note, however, that if multiple graphs are represented without
an @id, they will be merged on expansion. To prevent this,
use @none judiciously, and consider giving graphs
their own distinct identifier.

A documentLoader
can be useful in a number of contexts where loading remote documents can be problematic:

Remote context documents should be cached to prevent overloading the
location of the remote context for each request.
Normally, an HTTP caching infrastructure might be expected to handle this,
but in some contexts this might not be feasible.
A documentLoader implementation might provide separate logic for performing
such caching.

Non-standard URL schemes may not be widely implemented,
or may have behavior specific to a given application domain.
A documentLoader can be defined to implement document retrieval semantics.

Certain well-known contexts may be statically cached within a documentLoader implementation.
This might be particularly useful in embedded applications,
where it is not feasible, or even possible, to access remote documents.

For security purposes, the act of remotely retrieving a document may provide a signal of application behavior.
The judicious use of a documentLoader can isolate the application and reduce its online fingerprint.

5. Forms of JSON-LD

This section is non-normative.

As with many data formats, there is no single correct way to describe data in JSON-LD.
However, as JSON-LD is used for describing graphs, certain transformations can be used
to change the shape of the data, without changing its meaning as Linked Data.

Flattening is the process of extracting
embedded nodes to the top level of the JSON tree, and replacing the embedded
node with a reference, creating blank node identifiers as necessary. This
process is described further in § 5.3 Flattened Document Form.

Framed Document Form

Framing is used to shape
the data in a JSON-LD document, using an example frame document
which is used to both match the flattened data and show an example
of how the resulting data should be shaped. This
process is described further in § 5.4 Framed Document Form.

5.1 Expanded Document Form

This section is non-normative.

The JSON-LD 1.1 Processing Algorithms and API specification [JSON-LD11-API]
defines a method for expanding a JSON-LD document.
Expansion is the process of taking a JSON-LD document and applying a
context such that all IRIs, types, and values
are expanded so that the @context is no longer necessary.

5.2 Compacted Document Form

This section is non-normative.

The JSON-LD 1.1 Processing Algorithms and API specification [JSON-LD11-API] defines
a method for compacting a JSON-LD document. Compaction is the process
of applying a developer-supplied context to shorten IRIs
to terms or compact IRIs
and JSON-LD values expressed in expanded form to simple values such as
strings or numbers.
Often this makes it simpler to work with document as the data is expressed in
application-specific terms. Compacted documents are also typically easier to read
for humans.

The details of Compaction are described in the
Compaction algorithm in [JSON-LD11-API].
This section provides a short description of how the algorithm operates as a guide
to authors creating contexts to be used for compacting JSON-LD documents.

The purpose of compaction is to apply the term definitions, vocabulary mapping, default language,
and base IRI to an existing JSON-LD document to cause it to be represented in a form
that is tailored to the use of the JSON-LD document directly as JSON.
This includes representing values as strings, rather than value objects, where possible,
shortening the use of list objects into simple arrays, reversing the relationship
between nodes, and using data maps to index into multiple values instead of
representing them as an array of values.

The vocabulary mapping can be used to shorten IRIs that may be vocabulary relative
by removing the IRI prefix that matches the vocabulary mapping.
This is done whenever an IRI is determined to be vocabulary relative,
i.e., used as a property, or a value of @type,
or as the value of a term described as "@type": "@vocab".

5.2.2 Representing Values as Strings

This section is non-normative.

To be unambiguous, the expanded document form always represents nodes
and values using node objects and value objects.
Moreover, property values are always contained within an array, even when there is only
one value. Sometimes this is useful to maintain a uniformity of access,
but most JSON data use the simplest possible representation, meaning that
properties have single values, which are represented as strings
or as structured values such as node objects.
By default, compaction will represent values which are simple strings as strings,
but sometimes a value is an IRI, a date, or some other typed value for which
a simple string representation would loose information.
By specifying this within a term definition,
the semantics of a string value can be inferred from the definition
of the term used as a property.
See § 4.2 Describing Values for more details.

The compacted version will use string values for the defined terms
when the values match the term definition. Note that there is
no term defined for "plain", that is created automatically using
the vocabulary mapping.
Also, the other native values,
1 and true,
can be represented without defining a specific type mapping.

5.2.3 Representing Lists as Arrays

This section is non-normative.

As described in § 4.3.1 Lists,
JSON-LD has an expanded syntax for representing ordered values,
using the @list keyword.
To simplify the representation in JSON-LD, a term can be defined with
"@container": "@list" which causes all values of a
property using such a term to be considered ordered.

5.2.4 Reversing Node Relationships

This section is non-normative.

In some cases, the property used to relate two nodes may
be better expressed if the nodes have a reverse direction,
for example, when describing a relationship between
two people and a common parent.
See § 4.8 Reverse Properties for more details.

Reverse properties can be even more useful when combined with
framing, which can actually make node objects defined
at the top-level of a document to become embedded nodes.
JSON-LD provides a means to index such values, by defining
an appropriate @container definition within a term definition.

5.2.5 Indexing Values

This section is non-normative.

Properties with multiple values are typically represented using
an unordered array. This means that an application working
on an internalized representation of that JSON would need to
iterate through the values of the array to find a value matching
a particular pattern, such as a language-tagged string
using the language en.

5.2.6 Normalizing Values as Objects

This section is non-normative.

Sometimes it's useful to compact a document, but keep the
node object and value object representations.
For this, a term definition can set "@type": "@none".
This causes the Value Compaction algorithm to always use the object
form of values, although components of that value may be compacted.

The compacted version will use string values for the defined terms
when the values match the term definition.
Also, the other native values,
1 and true,
can be represented without defining a specific type mapping.

5.2.7 Representing Singular Values as Arrays

This section is non-normative.

Generally, when compacting, properties having only one value are
represented as strings or maps, while properties having
multiple values are represented as an array of strings or maps.
This means that applications accessing such properties need to be prepared
to accept either representation. To force all values to be represented
using an array, a term definition can set "@container": "@set".
Moreover, @set can be used in combination with other container settings,
for example looking at our language-map example from § 5.2.5 Indexing Values:

5.2.8 Term Selection

This section is non-normative.

When compacting, the Compaction algorithm will compact using a term
for a property only when the values of that property match the
@container, @type, and @language specifications for that term definition.
This can actually split values between different properties, all of which
have the same IRI. In case there is no matching term definition,
the compaction algorithm will compact using the absolute IRI of the property.

Note that the values that match the "integer", "english", "date", and "iri"
terms are properly matched, and that everything that does not explicitly
match is added to a property created using a compact IRI.

5.3 Flattened Document Form

This section is non-normative.

The JSON-LD 1.1 Processing Algorithms and API specification [JSON-LD11-API] defines
a method for flattening a JSON-LD document.
Flattening collects all
properties of a node in a single map and labels
all blank nodes with
blank node identifiers.
This ensures a shape of the data and consequently may drastically simplify the code
required to process JSON-LD in certain applications.

5.4 Framed Document Form

This section is non-normative.

The JSON-LD 1.1 Framing specification [JSON-LD11-FRAMING] defines
a method for framing a JSON-LD document. Framing is used to shape
the data in a JSON-LD document, using an example frame document
which is used to both match the flattened data and show an example
of how the resulting data should be shaped.

This frame document describes an embedding structure that would place
objects with type Library at the top, with objects of
type Book that were linked to the library object using
the contains property embedded as property values. It also
places objects of type Chapter within the referencing Book object
as embedded values of the Book object.

When using a flattened set of objects that match the frame components:

JSON-LD's media type also defines a
profile parameter which can be used to identify a
script element in an HTML document containing a frame.
The first script element
of type application/ld+json;profile=http://www.w3.org/ns/json-ld#frame
will be used to find a frame..

6. Modifying Behavior with Link Relationships

Certain aspects of JSON-LD processing can be modified using
HTTP Link Headers [RFC8288].
These can be used when retrieving resources that are not, themselves, JSON-LD,
but can be interpreted as JSON-LD by using information in a
Link Relation.

In other cases, a resource may be returned using a representation that cannot easily be interpreted
as JSON-LD. Normally, HTTP content negotiation
would be used to allow a client to specify a preference for JSON-LD over another representation,
but in certain situations, it is not possible or practical for a server to respond appropriately to such requests.
For this, an HTTP Link Header can be used to provide an alternate location for a document
to be used in place of the originally requested resource,
as described in § 6.2 Alternate Document Location.

6.1 Interpreting JSON as JSON-LD

Ordinary JSON documents can be interpreted as JSON-LD
by providing an explicit JSON-LD context document. One way
to provide this is by using referencing a JSON-LD
context document in an HTTP Link Header.
Doing so allows JSON to be unambiguously machine-readable without requiring developers to drastically
change their documents and provides an upgrade path for existing infrastructure
without breaking existing clients that rely on the application/json
media type or a media type with a +json suffix as defined in
[RFC6839].

In order to use an external context with an ordinary JSON document,
when retrieving an ordinary JSON document via HTTP, processors MUST
attempt to retrieve any JSON-LD document referenced by a
Link Header with:

rel="http://www.w3.org/ns/json-ld#context", and

type="application/ld+json".

The referenced document MUST have a top-level JSON object.
The @contextentry within that object is added to the top-level
JSON object of the referencing document. If an array
is at the top-level of the referencing document and its items are
JSON objects, the @context
subtree is added to all array items. All extra information located outside
of the @context subtree in the referenced document MUST be
discarded. Effectively this means that the active context is
initialized with the referenced external context. A response MUST NOT
contain more than one HTTP Link Header using the
http://www.w3.org/ns/json-ld#context link relation.

Other mechanisms for providing a JSON-LD Context MAY be described for other
URI schemes.

The JSON-LD 1.1 Processing Algorithms and API specification [JSON-LD11-API]
provides for an expandContext option for specifying
a context to use when expanding JSON documents programmatically.

The following example demonstrates the use of an external context with an
ordinary JSON document over HTTP:

Please note that JSON-LD documents
served with the application/ld+json
media type MUST have all context information, including references to external
contexts, within the body of the document. Contexts linked via a
http://www.w3.org/ns/json-ld#contextHTTP Link HeaderMUST be
ignored for such documents.

6.2 Alternate Document Location

Documents which can't be directly interpreted as JSON-LD can provide an alternate location containing JSON-LD.
One way to provide this is by referencing a JSON-LD document in an HTTP Link Header.
This might be useful, for example, when the URL associated with a namespace naturally
contains an HTML document, but the JSON-LD context associated with that URL is located elsewhere.

To specify an alternate location, a non-JSON resource
(i.e., one using a media type other than application/json or a derivative)
can return the alternate location using a Link Header with:

rel="alternate", and

type="application/ld+json".

A response MUST NOT contain more than one HTTP Link Header using the
alternate link relation with type="application/ld+json" .

Other mechanisms for providing an alternate location MAY be described for other
URI schemes.

The following example demonstrates the use of an alternate location with an
ordinary HTTP document over HTTP:

7.3 Locating a Specific JSON-LD Script Element

A specific
script element
within an HTML document may be located using
a fragment identifier matching the unique identifier
of the script element within the HTML document located by a URL (see [DOM]).
A JSON-LD processorMUST extract only the specified data block's contents
parsing it as a standalone JSON-LD document
and MUST NOT merge the result with any other markup from the same HTML document.

For example, given an HTML document located at http://example.com/document,
a script element identified by "dave" can be targeted using the URL
http://example.com/document#dave.

8. Data Model

JSON-LD is a serialization format for Linked Data based on JSON.
It is therefore important to distinguish between the syntax, which is
defined by JSON in [RFC8259], and the data model which is
an extension of the RDF data model [RDF11-CONCEPTS].
The precise details of how JSON-LD relates to the RDF data model are given in
§ 10. Relationship to RDF.

To ease understanding for developers unfamiliar with the RDF model, the
following summary is provided:

A graph
is a labeled directed graph, i.e., a set of nodes
connected by directed-arcs.

Every directed-arc is labeled with
an IRI or a blank node identifier. Within the JSON-LD syntax
these arc labels are called properties.
Whenever practical, a directed-arc SHOULD be labeled with an IRI.

Note

The use of blank node identifiers to label properties is obsolete,
and may be removed in a future version of JSON-LD.
Consider using a document-relative IRI, instead, such as #.

This effectively just prohibits unnested, empty node objects
and unnested node objects that contain only an @id.
A document may have nodes which are unrelated, as long as one or more
properties are defined, or the node is referenced from another node object.

An IRI (Internationalized Resource Identifier) is a string that conforms to the syntax
defined in [RFC3987]. IRIs used within a
graphSHOULD return a Linked Data document describing
the resource denoted by that IRI when being dereferenced.

Whenever a keyword is discussed in this grammar,
the statements also apply to an alias for that keyword.

Note

JSON-LD allows keywords to be aliased
(see § 4.1.6 Aliasing Keywords for details). For example, if the active context
defines the termid as an alias for @id,
that alias may be legitimately used as a substitution for @id.
Note that keyword aliases are not expanded during context
processing.

To avoid forward-compatibility issues, a termSHOULD NOT start
with an @ character
followed exclusively by one or more ALPHA characters (see [RFC5234])
as future versions of JSON-LD may introduce
additional keywords. Furthermore, the term MUST NOT
be an empty string ("") as not all programming languages
are able to handle empty JSON keys.

9.3 Frame Objects

A frame objectMAY include a default object as the value of any key
which is not a keyword.
Values of @defaultMAY include the value @null,
or an array containing only @null, in addition to other values
allowed in the grammar for values of entry keys expanding to IRIs.

9.5 Value Objects

A value objectMUST be a map containing the
@value key. It MAY also contain an @type,
an @language,
an @direction,
an @index, or an @context key but MUST NOT contain
both an @type and either @languageor @direction
keys at the same time.
A value objectMUST NOT contain any other keys that expand to an
IRI or keyword.

The value associated with the @value key MUST be either a
string, a number, true,
false or null.
If the value associated with the @type key
is @json, the value MAY be either an array or an object.

9.7 Lists and Sets

A list represents an ordered set of values. A set
represents an unordered set of values. Unless otherwise specified,
arrays are unordered in JSON-LD. As such, the
@set keyword, when used in the body of a JSON-LD document,
represents just syntactic sugar which is optimized away when processing the document.
However, it is very helpful when used within the context of a document. Values
of terms associated with an @set or @list container
will always be represented in the form of an array when a document
is processed—even if there is just a single value that would otherwise be optimized to
a non-array form in compacted document form.
This simplifies post-processing of the data as the data is always in a
deterministic form.

9.8 Language Maps

A language map is used to associate a language with a value in a
way that allows easy programmatic access. A language map may be
used as a term value within a node object if the term is defined
with @container set to @language,
or an array containing both @language and @set. The keys of a
language mapMUST be strings representing
[BCP47] language tags, the keyword@none,
or a term which expands to @none,
and the values MUST be any of the following types:

9.9 Index Maps

An index map allows keys that have no semantic meaning,
but should be preserved regardless, to be used in JSON-LD documents.
An index map may
be used as a term value within a node object if the
term is defined with @container set to @index,
or an array containing both @index and @set.
The values of the entries of an index mapMUST be one
of the following types:

Index Maps may also be used to map indexes to associated
named graphs, if the term is defined with @container
set to an array containing both @graph and
@index, and optionally including @set. The
value consists of the node objects contained within the named
graph which is indexed using the referencing key, which can be
represented as a simple graph object if the value does
not include @id, or a named graph if it includes @id.

If the value contains a property expanding to @id, its value MUST
be equivalent to the referencing key. Otherwise, the property from the value is used as
the @id of the node object value when expanding.

Id Maps may also be used to map graph names to their
named graphs, if the term is defined with @container
set to an array containing both @graph and @id,
and optionally including @set. The value consists of the
node objects contained within the named graph
which is named using the referencing key.

If the value contains a property expanding to @type, and its value
is contains the referencing key after suitable expansion of both the referencing key
and the value, then the node object already contains the type. Otherwise, the property from the value is
added as a @type of the node object value when expanding.

If the expanded term definition contains the @containerkeyword, its value MUST be either
@list,
@set,
@language,
@index,
@id,
@graph,
@type, or be
null
or an array containing exactly any one of those keywords, or a
combination of @set and any of @index,
@id, @graph, @type,
@language in any order
.
@container may also be an array
containing @graph along with either @id or
@index and also optionally including @set.
If the value
is @language, when the term is used outside of the
@context, the associated value MUST be a language map.
If the value is @index, when the term is used outside of
the @context, the associated value MUST be an
index map.

The unaliased @container keyword MAY be used as a key in an expanded term definition.
Its value MUST be either
@list,
@set,
@language,
@index,
@id,
@graph,
@type, or be
null,
or an array containing exactly any one of those keywords, or a
combination of @set and any of @index,
@id, @graph, @type,
@language in any order.
The value may also be an array
containing @graph along with either @id or
@index and also optionally including @set.

@context

The @context keyword MUST NOT be aliased, and MAY be used as a key in the following objects:

The @list keyword MAY be aliased and MUST be used as a key in a list object.
The unaliased @listMAY be used as the value of the @container key within an expanded term definition.
Its value MUST be one of the following:

10. Relationship to RDF

JSON-LD is a
concrete RDF syntax
as described in [RDF11-CONCEPTS]. Hence, a JSON-LD document is both an
RDF document and a JSON document and correspondingly represents an
instance of an RDF data model. However, JSON-LD also extends the RDF data
model to optionally allow JSON-LD to serialize
generalized RDF Datasets.
The JSON-LD extensions to the RDF data model are:

In JSON-LD lists use native JSON syntax, either contained in a
list object, or described as such within a context. Consequently, developers
using the JSON representation can access list elements directly rather than
using the vocabulary for collections described in [RDF-SCHEMA].

Summarized, these differences mean that JSON-LD is capable of serializing any RDF
graph or dataset and most, but not all, JSON-LD documents can be directly
interpreted as RDF as described in RDF 1.1 Concepts [RDF11-CONCEPTS].

Authors are strongly encouraged to avoid labeling properties using blank node identifiers,
instead, consider one of the following mechanisms:

Publishers supporting both dataset and graph syntaxes have to ensure that
the primary data is stored in the default graph to enable consumers that do not support
datasets to process the information.

10.1 Serializing/Deserializing RDF

This section is non-normative.

The process of serializing RDF as JSON-LD and deserializing JSON-LD to RDF
depends on executing the algorithms defined in
RDF Serialization-Deserialization Algorithms
in the JSON-LD 1.1 Processing Algorithms and API specification [JSON-LD11-API].
It is beyond the scope of this document to detail these algorithms any further,
but a summary of the necessary operations is provided to illustrate the process.

The procedure to deserialize a JSON-LD document to RDF involves the
following steps:

Expand the JSON-LD document, removing any context; this ensures
that properties, types, and values are given their full representation
as IRIs and expanded values. Expansion
is discussed further in § 5.1 Expanded Document Form.

The process of serializing RDF as JSON-LD can be thought of as the
inverse of this last step, creating an expanded JSON-LD document closely
matching the triples from RDF, using a single node object
for all triples having a common subject, and a single property
for those triples also having a common predicate. The result may
then be framed by using the
Framing Algorithm
described in [JSON-LD11-FRAMING] to create the desired object embedding.

10.2 The rdf:JSON Datatype

RDF provides for JSON content as a possible literal value.
This allows markup in literal values.
Such content is indicated in a graph using a literal whose datatype is set to rdf:JSON.

Strings MUST be serialized with Unicode codepoints from U+0000 through U+001F
using lower case hexadecimal Unicode notation (\uhhhh) unless in the set
of predefined JSON control characters U+0008, U+0009,
U+000A, U+000C or U+000D
which SHOULD be serialized as \b, \t, \n, \f and \r respectively.
All other Unicode characters SHOULD be serialized "as is", other than
U+005C (\) and U+0022 (")
which SHOULD be serialized as \\ and \" respectively.

Issue

The JSON Canonicalization Scheme [JCS]
is an emerging standard for JSON canonicalization
not yet ready to be referenced.
When a JSON canonicalization standard becomes available,
this specification will likely be updated to require such a canonical representation.
Users are cautioned from depending on the
JSON literal lexical representation as an RDF literal,
as the specifics of serialization may change in a future revision of this document.

Despite being defined as a set of strings,
this value space is considered distinct from the value space of xsd:string,
in order to avoid side effects with existing specifications.

Datatypes based on this namespace allow round-tripping of JSON-LD documents using base direction,
although the mechanism is not otherwise standardized.

The Deserialize JSON-LD to RDF Algorithm
can be used with the rdfDirection option
set to i18n-datatype to generate RDF literals using the i18n base to create an IRI
encoding the base direction along with optional language tag (normalized to lower case)
from value objects containing @direction by appending to https://www.w3.org/ns/i18n#
the value of @language, if any, followed by an underscore ("_") followed
by the value of @direction.

For improved interoperability, the language tag is normalized to
lower case when creating the datatype IRI.

(Feature at Risk) Issue

This feature is experimental, as RDF does not have a
standard way to represent base direction in RDF literals.
A future RDF Working Group may support base direction differently.
The JSON-LD Working Group solicits feedback from the community on the
usefulness of these transformations.

The following example shows two statements with literal values of i18n:ar-EG_rtl,
which encodes the language tag ar-EG and the base direction rtl.

10.4 The rdf:CompoundLiteral class and the rdf:language and rdf:direction properties

This section is non-normative.

This specification defines the rdf:CompoundLiteral class, which is in the domain
of rdf:language and rdf:direction to be used for describing RDF literal values
containing base direction and a possible language tag to be associated with the
string value of rdf:value on the same subject.

rdf:CompoundLiteral

A class representing a compound literal.

rdf:language

An RDF property.
The range of the property is an rdfs:Literal, whose value MUST be a well-formed [BCP47] language tag.
The domain of the property is rdf:CompoundLiteral.

rdf:direction

An RDF property.
The range of the property is an rdfs:Literal, whose value MUST be either "ltr" or "rtl".
The domain of the property is rdf:CompoundLiteral.

For improved interoperability, the language tag is normalized to
lower case when creating the datatype IRI.

(Feature at Risk) Issue

This feature is experimental, as RDF does not have a
standard way to represent base direction in RDF literals.
A future RDF Working Group may support base direction differently.
The JSON-LD Working Group solicits feedback from the community on the
usefulness of these transformations.

The following example shows two statements with compound literals
representing strings with the language tagar-EG and base directionrtl.

11. Security Considerations

Future versions of this specification
may incorporate subresource integrity [SRI] as a means of ensuring that cached and retrieved
content matches data retrieved from remote servers; see issue 86.

12. Privacy Considerations

The retrieval of external contexts can expose the operation of a JSON-LD processor,
allow intermediate nodes to fingerprint the client application through introspection of retrieved resources
(see [fingerprinting-guidance]),
and provide an opportunity for a man-in-the-middle attack.
To protect against this, publishers should consider caching remote contexts for future use,
or use the documentLoader
to maintain a local version of such contexts.

13. Internationalization Considerations

As JSON-LD uses the RDF data model, it is restricted by design in its ability to
properly record JSON-LD Values which are strings with left-to-right or right-to-left direction indicators.
Both JSON-LD and RDF provide a mechanism for specifying the language associated with
a string (language-tagged string), but do not provide a means of indicating
the base direction of the string.

The issue of properly representing base direction in RDF is not something that
this Working Group can handle, as it is a limitation or the core RDF data model.
This Working Group expects that a future RDF Working Group will consider the matter
and add the ability to specify the base direction of language-tagged strings.

Until a more comprehensive solution can be addressed in a future version of this
specification, publishers should consider this issue when representing strings
where the base direction of the string cannot otherwise be correctly inferred
based on the content of the string.
See [string-meta] for a discussion best practices for
identifying language and base direction for strings used on the Web.

A. Image Descriptions

A.1 Linked Data Dataset

The image consists of three dashed boxes, each describing a different
linked data graph. Each box consists of shapes linked with arrows describing
the linked data relationships.

The first box is titled "default graph: <no name>" describes two
resources: http://example.com/people/alice and http://example.com/people/bob
(denoting "Alice" and "Bob" respectively), which are
connected by an arrow labeled schema:knows which describes
the knows relationship between the two resources. Additionally, the "Alice" resource is related
to three different literals:

Alice

an RDF literal with no datatype or language.

weiblich | de

an language-tagged string with the value "weiblich" and language tag "de".

female | en

an language-tagged string with the value "female" and language tag "en".

The second and third boxes describe two named graphs, with the graph names
"http://example.com/graphs/1" and "http://example.com/graphs/1", respectively.

The second box consists of two resources:
http://example.com/people/alice and http://example.com/people/bob
related by the schema:parent relationship, and names the
http://example.com/people/bob "Bob".

The third box consists of two resources, one
named http://example.com/people/bob and the other unnamed.
The two resources related to each other using schema:sibling relationship
with the second named "Mary".

B. Relationship to Other Linked Data Formats

This section is non-normative.

The JSON-LD examples below demonstrate how JSON-LD can be used to
express semantic data marked up in other linked data formats such as Turtle,
RDFa, and Microdata. These sections are merely provided as
evidence that JSON-LD is very flexible in what it can express across different
Linked Data approaches.

B.1 Turtle

This section is non-normative.

The following are examples of transforming RDF expressed in [Turtle]
into JSON-LD.

B.1.1 Prefix definitions

The JSON-LD context has direct equivalents for the Turtle
@prefix declaration:

B.1.3 Conversion of native data types

In JSON-LD numbers and boolean values are native data types. While [Turtle]
has a shorthand syntax to express such values, RDF's abstract syntax requires
that numbers and boolean values are represented as typed literals. Thus,
to allow full round-tripping, the JSON-LD 1.1 Processing Algorithms and API specification [JSON-LD11-API]
defines conversion rules between JSON-LD's native data types and RDF's
counterparts. Numbers without fractions are
converted to xsd:integer-typed literals, numbers with fractions
to xsd:double-typed literals and the two boolean values
true and false to a xsd:boolean-typed
literal. All typed literals are in canonical lexical form.

Note that this interpretation differs from [Turtle],
in which the literal 2.78 translates to an xsd:decimal.
The rationale is that most JSON tools parse numbers with fractions as
floating point numbers,
so xsd:double is the most appropriate datatype to render them back in RDF.

C. IANA Considerations

This section has been submitted to the Internet Engineering Steering
Group (IESG) for review, approval, and registration with IANA.

application/ld+json

Type name:

application

Subtype name:

ld+json

Required parameters:

N/A

Optional parameters:

profile

A non-empty list of space-separated URIs identifying specific
constraints or conventions that apply to a JSON-LD document according to [RFC6906].
A profile does not change the semantics of the resource representation
when processed without profile knowledge, so that clients both with
and without knowledge of a profiled resource can safely use the same
representation. The profile parameter MAY be used by
clients to express their preferences in the content negotiation process.
If the profile parameter is given, a server SHOULD return a document that
honors the profiles in the list which it recognizes,
and MUST ignore the profiles in the list which it does not recognize.
It is RECOMMENDED that profile URIs are dereferenceable and provide
useful documentation at that URI. For more information and background
please refer to [RFC6906].

All other URIs starting with http://www.w3.org/ns/json-ld
are reserved for future use by JSON-LD specifications.

Other specifications may publish additional profile parameter
URIs with their own defined semantics.
This includes the ability to associate a file extension with a profile parameter.

When used as a media type parameter [RFC4288]
in an HTTP Accept header [RFC7231],
the value of the profile parameter MUST be enclosed in quotes (") if it contains
special characters such as whitespace, which is required when multiple profile URIs are combined.

When processing the "profile" media type parameter, it is important to
note that its value contains one or more URIs and not IRIs. In some cases
it might therefore be necessary to convert between IRIs and URIs as specified in
section 3 Relationship between IRIs and URIs
of [RFC3987].

Since JSON-LD is intended to be a pure data exchange format for
directed graphs, the serialization SHOULD NOT be passed through a
code execution mechanism such as JavaScript's eval()
function to be parsed. An (invalid) document may contain code that,
when executed, could lead to unexpected side effects compromising
the security of a system.

When processing JSON-LD documents, links to remote contexts and frames are
typically followed automatically, resulting in the transfer of files
without the explicit request of the user for each one. If remote
contexts are served by third parties, it may allow them to gather
usage patterns or similar information leading to privacy concerns.
Specific implementations, such as the API defined in the
JSON-LD 1.1 Processing Algorithms and API specification [JSON-LD11-API],
may provide fine-grained mechanisms to control this behavior.

JSON-LD contexts that are loaded from the Web over non-secure connections,
such as HTTP, run the risk of being altered by an attacker such that
they may modify the JSON-LD active context in a way that
could compromise security. It is advised that any application that
depends on a remote context for mission critical purposes vet and
cache the remote context before allowing the system to use it.

Given that JSON-LD allows the substitution of long IRIs with short terms,
JSON-LD documents may expand considerably when processed and, in the worst case,
the resulting data might consume all of the recipient's resources. Applications
should treat any data with due skepticism.

As JSON-LD places no limits on the IRI schemes that may be used,
and vocabulary-relative IRIs use string concatenation rather than
IRI resolution, it is possible to construct IRIs that may be
used maliciously, if dereferenced.

Interoperability considerations:

Not Applicable

Published specification:

http://www.w3.org/TR/json-ld

Applications that use this media type:

Any programming environment that requires the exchange of
directed graphs. Implementations of JSON-LD have been created for
JavaScript, Python, Ruby, PHP, and C++.

Requests the server to return the requested resource as JSON-LD
in compacted document form.
As no explicit context resource is specified, the server compacts
using an application-specific default context.

Example 168: HTTP Request with profile requesting a compacted document with a reference to a compaction context

An expanded term definition can now have an
@nest property, which identifies a term expanding to
@nest which is used for containing properties using the same
@nest mapping. When expanding, the values of a property
expanding to @nest are treated as if they were contained
within the enclosing node object directly.

The JSON syntax has been abstracted into an internal representation
to allow for other serializations that are functionally equivalent
to JSON.

The value for @container in an expanded term definition
can also be an array containing any appropriate container
keyword along with @set (other than @list).
This allows a way to ensure that such property values will always
be expressed in array form.

Values of properties where the associated term definition
has @container set to @graph are interpreted as
implicitly named graphs, where the associated graph name is
assigned from a new blank node identifier. Other combinations
include ["@container", "@id"], ["@container", "@index"] each also
may include "@set", which create maps from the
graph identifier or index value similar to index maps
and id maps.

F. Changes since JSON-LD Community Group Final Report

Values of @type, or an alias of @type, may now have their @container set to @set
to ensure that @typeentries are always represented as an array. This
also allows a term to be defined for @type, where the value MUST be a map
with @container set to @set.